1. Field of the Invention
The present invention relates to glass processing equipment with dynamic production control. Specifically, the invention relates to a dynamic, lean Insulated Glass Unit assembly line scheduler.
2. Background Information
Insulated Glass Units—IGU
Insulated glass units are formed by multiple glass panes or “lites” assembled into units. The units are also commonly referred to as merely insulated glass (IG), or insulated glass units (IGU) in the United States and Australia. They are also commonly referred to as double glazing, double glazed units in Europe. All of the terms or phrases reference a structure having multiple panes, typically of glass, or “lites” assembled into units. IGUs generally use the thermal and acoustic insulating properties of a gas, and/or partial vacuum, contained in the space between the lites formed by the unit. IGUs provide excellent insulation properties without sacrificing transparency. Transparency is generally a critical measurement in most such IGUs and is also referenced or measured as visual transmittance or VT. Commercially, most IGUs are “double glazed” meaning there are two panes or lites, but IGUs with three panes or lites (or more), i.e. “triple glazing” is becoming more common due to higher energy costs. For performance and evaluation standards see “ASTM E2190-08” which is the standard specification for “Insulating Glass Unit Performance and Evaluation”.
IGUs may be framed in a sash, frame or in a curtain wall. IGUs are manufactured with glass lites typically in range of thickness from 3 mm to 10 mm, although greater widths are known for special applications. Laminated or tempered glass lites may also be used as part of the construction. Most IGUs are manufactured with the same thickness of glass lites used on both (or all) panes but special applications such as acoustic attenuation or security may require wide ranges of thicknesses for different panes to be incorporated in the same IGU.
While clear glass is the most common glass lite component of IGUs, tinted glass is be used in some IGUs to reduce solar heat gain or as an architectural feature. Other transparent material could also be used, but glass is certainly the most common. The principle colors available for tiniting the lites are bronze, gray and green. The degree of tint depends on both the composition of the glass and the thickness of the lite. Tinted glass is usually placed on the exterior of the IGU. The heat and sound insulation properties or scratch resistance or other properties of an IGUs may also be improved by the use of a film or coating applied to its surface. This film is typically made of polyester or metal, and may give the window a reflective appearance.
Further, Low-Emissivity Glass lites are also used in IGUs and is glass that has a thin coating, often of metal, on the glass within its airspace that reflects thermal radiation or inhibits its emission reducing heat transfer through the glass. A basic low-e coating allows solar radiation to pass through into a room.
There are two types of low-e coatings currently widely available, “hard-coat” and “soft-coat”. See, for example, U.S. Pat. Nos. 3,537,944, 3,978,272, 4,098,956, 4,534,841, 4,902,580, 5,543,229, 6,306,525, 6,355,334, 6,650,478, 6,838,159, 7,063,893, 7,727,632, 7,758,915 which disclose various glass coatings and are incorporated herein by reference. Hard-coat glass lites are manufactured by applying molten tin to the glass surface as the glass sheets are being manufactured. The tin bonds to the surface of the glass and forms a relatively thick coating. Hard-coat glass lites are considered a medium performance coating since the emissivity is greater compared to the soft-coat product. One advantage of hard-coat glass is that it does not require special handling in the IGU assembly line to maintain the surface's coating integrity and does not scratch easily. It does require that the glass surface in contact with the spacer be abraded to improve adhesion of the sealant. Soft-coat glass uses vacuum deposition to apply a thin metallic coating to the glass surface as an additional manufacturing step. The coating is fragile compared to hard coat glass, requiring special handling and storage for both the manufacturing process and IGU fabrication. It has been suggested that selecting a soft-coat glass over a hard-coat glass improves thermal performance of the IGU by about 13%. Most low-emissivity glass sold for IGU manufacturing is of the hard-coat type.
The glass panes of an IGU are separated by a spacer. Most spacers are constructed of either thin gauge steel or aluminum for thermal expansion stability or cost reasons. The spacer may alternatively be constructed of fiberglass or use a hybrid design of metal and plastic. The spacer may further be filled with desiccant to remove moisture trapped in the air space during manufacturing, preventing condensation from forming on an inner glass pane surface when the temperature falls below the dew point. U.S. Pat. Nos. 5,361,476, 5,640,828, 6,360,420, 6,823,644, 7,449,224 and U.S. Patent Publication Numbers 2008-0134627, 2009-0107085, 2009-0120018, 2009-0120019, 2009-0120035, 2009-0120036, disclose spacer designs that are incorporated herein by reference.
IGU thickness is often a compromise between maximizing insulating value and the ability of the framing system used to carry the unit and weight concerns. These issues can be advantageously addressed with other considerations, for example, a perfect vacuum provides the most thermal insulation value. Alternatively, a technique called evacuated glazing can be used to drastically reduce heat transfer through convection and conduction. These IGUs have most of the air removed from the space between the panes, leaving a partial vacuum. Another alternative is to replace air in the space with inert gases such as argon, as argon has a thermal conductivity 67% that of air, or krypton, where krypton has about half the conductivity of argon, or even xenon to increase the insulating performance. These gasses have a higher mass (density) compared to air but have costs that increase exponentially with the type of gas used, xenon being the most expensive. In general, the more effective a fill gas is at its optimum thickness, the thinner the optimum thickness is.
A muntin is technically described as a strip of material (often wood or metal or even plastic) separating and holding panes of glass lites in a window. Muntins are also called “glazing bars”, “astragals”, “muntin bars,” “false muntins” “grilles” or, somewhat confusingly, “mullions”. Many companies in the U.S. use the term “grille” when referring to a set of decorative muntin bars added to give a sash the appearance of a “true divided light” sash. In the IGU field decorative muntins
IG Assembly Lines
IGUs are manufactured on a made-to-order basis on factory production lines, such as the Billco Manufacturing Vertical I.G. line, or the GED Intercept™ IG line or the Lisec Vertical I.G. Line. See also U.S. Pat. Nos. 4,434,024, 4,885,926, 4,961,270, 4,961,816, 5,173,148, 5,394,725, 5,823,732, 5,932,062, 6,038,825, 6,068,720, 6,148,890, 6,279,292, 6,329,030, 6,378,586, 6,609,611, 6,793,971 and U.S. Patent Publication Number 2007-0074803, 2009-0014493 which are incorporated herein by reference and which disclose IGU production lines or related components and/or developments therefore.
In any I.G. assembly line, for each individual IGU, the width and height dimensions of each lite, the thickness of the glass lites, the type of glass for each glass lite, the specific spacer, the inner pane gas (e.g., air, argon, xenon, krypton), if any, and treatment (i.e. partial vacuum level), spacer type, muntin type, if any, must be supplied to the I.G. assembly line. On the I.G. assembly line, spacers of specific thicknesses are cut and assembled into the required overall width and height dimensions and filled with desiccant. On an earlier or upstream glass cutting line, glass panes of the relevant types are cut to size and supplied to the IG line. On the I.G. line the glass lites are washed to be optically clear. An adhesive sealant, such as polyisobutylene or PIB for short, is applied to the face of the spacer on each side and the appropriate lites pressed against the spacer. If the IGU is gas filled, two holes may be drilled into the spacer of the assembled unit, lines are attached to draw out the air out of the space and replaced with the desired gas, with the drilled holes being subsequently sealed. Alternatively the IG line may have what is known as an “online gas filler”, which removes the need to drill holes in the spacer. The units are then sealed on the edge side using an outer sealant such as either polysulphide or silicone sealant or similar material to prevent humid outside air from entering the unit. The desiccant will remove traces of humidity from the air space so that no water appears on the inside faces of the glass panes facing the air space during cold weather. Some manufacturers have developed specific processes that combine the spacer and desiccant into a single step application system. Internal or external muntins can be applied on the IG line which may include the drilling of attachment holes in selected locations.
IG Line Control
Existing I.G. lines typically utilize a production control system designed to control the I.G. line processes and to identify or schedule the lites that need to be introduced into the I.G. line. The result of this control system is known as a line schedule. The schedule created will identify what order the specific IGUs will be produced, which in addition to the specific order the lites need to be introduced into the I.G. Line, the schedule will also identify what spacers need to be used for a specific piece, what muntins are to be used, what washing parameters, sealant parameters, gas parameters, and other operating parameters for the I.G. line.
Some of the changes in specific IGUs require time consuming adjustments to be made to the I.G. line. For example, in some I.G. lines, a change in the style or type of spacer used on a designated IGU can cause a delay, typically 2-20 minutes, in the line processing while the spacer type is swapped out in the specific location of the I.G. Changes in the muntin types can often require a change in drilling jigs used on the I.G. line. Changes in the gas type may likewise require a time consuming switch out of items on the I.G. Line. Other IGU types can result in other time consuming change outs on the I.G. line and these examples are merely representative.
Within the meaning of this application an “I.G. assembly line change out” represents any IG assembly line change in stock material or operating parameter that requires the I.G. line to pause for a measurable period of time before continuing to process IGUs. The meaning of an I.G. assembly line change out may be more clear as compared to an “on the fly” parameter (or stock) change between different IGUs. For example a change in glass lite size between IGUs on the IGU assembly line may require only an adjustment of cleaning brush locations which can be shifted between components without pausing the line. An on the fly adjustment of the IG assembly line will define the IGUs as of the same general type. Distinct types of IGUs within the meaning of this application are those that require a IG assembly line change out to be performed between their respective assemblies.
There remains a need in the art to improve the IG Line schedulers to adequately balance the change out requirements with order cycle time efficiency. It is an object of the present invention to improve the efficiencies of IGU production lines incorporating an IG Line Scheduler.